AWWA ACE59872

To meet the anticipated requirements of the Stage II Disinfectant/Disinfection Byproducts Rule (D/DBPR),the Cobb County-Marietta Water Authority conducted a pilot study at the Hugh A. Wyckoff WaterTreatment Plant (WTP) to examine the effects of ozone/biofiltration, chlorine dioxide preoxidation, magneticion exchange (MIEX®), and post-filter nanofiltration (NF) on the removal of disinfection byproduct (DBP)precursor material. The study showed that ozone/biofiltration was ineffective in reducing totaltrihalomethane (TTHMFP) and haloacetic acid formation potential (HAA5FP), and that chlorine dioxidepreoxidation would be sufficient to meet the Stage I D/DBPR requirements. The MIEX and post-filter NFalternatives demonstrated incremental improvement in the removal that was already being achieved byconventional treatment; therefore, MIEX and post-filter NF were examined further as options to ensure thatthe Authority can achieve the Stage II requirements.The two treatment alternatives were then compared to determine which would be the best alternative toimplement at the Wyckoff WTP. The examination included both economic and non-economic factors,including construction cost, operations and maintenance (O&M) cost, system reliability, processperformance, design, and implementation factors. Key process design considerations included splittreatment, coagulant reduction, concentrate treatment and disposal, flux and recovery rate optimization, andmembrane fouling.The major difference between the two alternatives was that post-filter NF was significantly less expensive tobuild and operate. This was due to the fact that a post-filter NF plant could treat only 26.5 percent of theflow and still achieve the DBP treatment goals. A MIEX facility large enough to treat the entire 104 milliongallons-per-day (mgd) capacity of the plant, after the next plant expansion, was required to meet the samegoals. Therefore, the ability to treat a fraction of the flow made post-filter NF the most economic option ofthe two examined. The estimated construction cost for post-filter nanofiltration was approximately $33million versus the MIEX process that was estimated at approximately $47 million. Additionally, post-filterNF was found to be significantly less expensive to operate, with an estimated annual O&M cost of $1.8million versus the MIEX process at $4.2 million. Based on an average daily flow of 70 mgd, the cost per1,000 gallons (including the amortized capital cost) was estimated to be $0.20 for post-filter NF versus $0.34for MIEX. Includes tables.

Product Details

Edition:

Vol. - No.

Published:

06/17/2004

Number of Pages:

20

File Size:

1 file , 560 KB